Vast quantities of natural soil have been contaminated with toxic and dangerous materials such as gasoline, diesel oil, cleaning solvents and the like. Until recently, little effort was exerted in decontaminating natural soils. However, it has now been realized that the presence of contaminants such as gasoline, diesel fuel, cleaning fluids, solvents and the like in soil pose tremendous environmental and health hazards. For example, there is increasing evidence that many organic liquids that contaminate soils are toxic and carcinogenic and find their way into drinking water formations from contaminated soils. Additionally, there is increasing evidence that organic contaminants from contaminated soil also find their way into rivers and streams to pollute and contaminate such waters thereby having an adverse affect on fish and wildlife.
Previous efforts to decontaminate soil that is contaminated with vaporizable contaminants have been directed to a variety of procedures. For example, various types of solvent extraction or washing procedures have been utilized in an attempt to wash the contaminants from the soil. Aside from being quite costly, such washing techniques have not been overly successful in removing such contaminants from soil. Other methods have involved heating soil in an attempt to vaporize the contaminants and drive the contaminants from the soil. Such prior heating processes have also been only partially successful. For example, heating processes that have involved heated kilns have not been too successful because of poor heat transfer, the tendency of moist soils to "ball up", dust formation and the like.
Recently, U.S. Pat. No. 4,738,206 issued to John W. Noland, wherein a method and apparatus for utilizing a heating vessel with a heated screw conveyor to heat soil as it is moved through the vessel to "vapor strip" contaminants from the soil. While the Noland method and appartus were improvements over previous methods and apparatus for decontaminating soil, they have severe operating problems. For example, the Noland method and apparatus provide for the exclusion of oxygen or air inside the heated stripping chamber. This necessity to exclude air from the heated chamber in the Noland method and apparatus poses severe operating problems in that air locks, seals in other apparatus have to be utilized to rigorously exclude the entry of air into the Noland heated chamber. It is therefore apparent that there is a need for a simplified and improved method and apparatus for decontaminating natural soil that has been contaminated with vaporizable contaminates.
It is therefore an object of this invention to provide an improved method and apparatus for decontaminating soil. It is another object of this invention to provide an improved method and apparatus for removing vaporizable contaminants from soil and safely disposing of such contaminants. It is yet another object of this invention to provide an improved method and apparatus for removing vaporizable contaminants from soil by passing the contaminated soil through a heated vessel while controlling the amount of oxygen in the vessel to prevent explosions and fires.
Additional objects and advantages of the invention described herein will be apparent to those skilled in the art upon an examination of the following specification and drawings.